Plasma calcium concentrations were measured in 18 patients suffering from acute myocardial infarction. Estimations were performed for several days after admission to hospital and a fall in plasma calcium was observed in 13 cases. Plasma albumin levels also decreased over this period, and correction of plasma calcium values to a fixed albumin level removed the apparent tendency to hypocalcaemia in these patients. Three patients with myocardial ischaemia showed similar decreases in plasma calcium and albumin. The observed changes are probably related to confinement to bed.